1. Field of the Invention
The present invention relates to an apparatus for the detection and discrimination of targets in a marine environment, but more specifically, it relates to a clutter suppression apparatus that substantially eliminates false alarms while detecting the presence of a target in the presence of sea clutter on a rapid basis.
2. Description of the Prior Art
There is a need in the prior art to provide ships with the capability to detect low altitude threats such as sea skimmer missiles. In general, present day radar systems are limited in this ability because of multipath and sea clutter problems. It is also known that the foregoing problems exist with passive infrared detection systems like those contemplated for use with the present invention. However, these passive infrared detection systems do provide other advantages over radar systems, such as high accuracy designation, resolution of closely spaced targets and emission control utility. Nevertheless, there is a need in the prior art to develop a wide range of background normalization and clutter suppression schemes to improve the surveillance capability of existing infrared search and surveillance systems.
To provide adequate surveillance for shipboard use, the passive infrared (electro-optic) system must be able to detect targets at ranges sufficient to allow for timely hand-over to fire control or weapons systems for threat neutralization. Hence, the basic function of an electro-optics surveillance system is to detect a target, sometimes in the presence of severe background clutter, confirm that the target is real, determine the coordinates (r, .theta., .phi.) of the target and then hand over these coordinates to a tracking or fire control system at a range sufficient to allow time for an appropriate weapons response. The variables r, .theta., and .phi. are the target range, elevation and azimuth, respectively. The requirements of the active rangefinder portion of an infrared search and surveillance system depend, in large measure, on the precision of the passive detection system in elevation and azimuth. Further, in order to hit the target, it is necessary to aim the rangefinder beam at the target with adequate precision and to satisfy the temporal constraints associated with the particular design configuration of the detection system and its various subsystems, e.g., laser beam aiming device, laser rangefinder device and target detection device in which the present invention can be employed. A laser beam aiming/rangefinder device suitable for use with the present invention is disclosed in the above cited related application. Consequently, there is a need in the prior art to detect a target in the presence of severe background clutter but yet be able to hand-over the coordinates of the target to a tracking or fire control system substantially instantaneously.
The apparatus, according to the present invention, operates on video data that has been digitized. The digitized video data can be generated using a detector block containing a row of suitable infrared detector elements upon which is projected the moving image to be processed so that the row of detectors lies crosswise to the motion of the swept image. Thus, each detector row originates a channel of video data. The simultaneous production of parallel video channels by these detectors defines the complete target video data with which the apparatus according to the present invention operates. After suitable amplification, each channel is digitized by a digitizer producing (n) channels of target digital video information. The rate at which the digitizer produces new digital samples is determined by a system clock pulse train derived from the rotation of a scanning head and therefore synchronized thereto. This motion is read by a shaft encoder which produces a pulse (azimuth clock) with a pulse for the passage of every useable revolution element of the optical system. These shaft encoder pulses are used to time the action of the video digitizers and the action of the apparatus according to the present invention. These pulses are also counted in an azimuthal counter which then provides a coded count which indicates instantaneous direction "of look" for the scanner. This count is reset to zero by a fiduciary mark which is a part of the shaft encoder and ensures an absolute meaning for the azimuthal direction information. For a better understanding of suitable elevational and azimuthal timing schemes, refer to the aforementioned related application.
Based on the foregoing, there is a need in the prior art to interface target locating and similar devices to an electronic processor configured according to the present invention capable of simultaneous handling of (n) channels of target video data to perform a manipulation thereon according to a predetermined algorithm so as to emphasize those areas of the imaged area containing small targets of appreciable contrast to the background area.
The prior art, as indicated hereinabove, include advances in laser beam aiming devices, laser rangefinder devices and even image detection devices including image processors as related to background clutter suppression. However, insofar as can be determined, no prior art image processor for background clutter supression incorporates all of the features and advantages of the present invention.